Heating structures such as an electric heating blanket or a normal heating blanket have been widely used in the markets presently, for the purpose of getting an object of adjusting and controlling temperature, a PTC (positive temperature coefficient) element or an NTC element are taken as a sensing structure; the mode of using such heating structures for heating in cooperating with heat emitting lines thus is widely used.
As is depicted in FIG. 7 showing a U.S. Pat. No. 5,861,610 of which the main technical feature is to have a core “a” wound therearound with a heating conductor “a1”, a second insulating layer “a2”, a sensing wire “a3” and a first insulating layer “a4”, the sensing wire “a3” is made of PTC material (nickel alloy). Because of the characteristic of the PTC element, when the temperature of the sensing wire “a3” is raised following heating of the heating conductor “a1”, or the electric resistance of the sensing wire “a3” is changed by high temperature, a comparing circuit in a controller will do comparison, then the amount of current of the heating conductor “a1” will be adjusted according to the result of comparison, so that heat emitting temperature can be controlled within the range set by a user.
The above stated technique has been disclosed by U.S. Pat. Nos. 6,300,597, 6,310,322 and 6,768,086. We can see from the above approved patents that, it is quite popular presently to use PTC elements on the techniques of temperature controlling and detecting, such as is depicted in FIG. 8 showing a U.S. Pat. No. 7,138,611. In which a microprocessor “b” detects changing of the phase shifts of two shaping circuits “b1”, “b2” at set times to control turning on/off of a triggering switch “b3”, in order that a PTC element “b4” continuously heat or lower temperature, and thereby a heat emitting line can be kept within a predetermined working temperature range. Thereby heat emitting temperature of the heat emitting line can be controlled effectively to provide guarantee of safety. A U.S. Pat. No. 7,180,037 similarly detects changing of phase shift taking advantage of the characteristic of an NTC element to control the heat emitting temperature of the heat emitting line.
However, any of the above stated heat emitting structures must be input with electric current of over 100 volts to get the heating effect; hence although there is a perfect protecting circuit, danger of line damage or circuit fault can still exists, thereby people are exposed in the danger of electric shock. And when people stay outdoors or in cars, they are hard to get the alternative electric current from indoors, although they can change direct electric current to alternative electric current by an electric power inverter, the volume of the power inverter will be largely increased for the purpose of generating sufficient electric power to heat a heat emitting structure such as an electric heating blanket or a normal heating blanket. This not only is space wasting, but also is inconvenient in use.
In view of the this, and for getting rid of the above defects to make a heat emitting device and its method of temperature controlling able to perform heating with a power source using lower voltage direct current, and to make a user able to avoid electric shock and use the device conveniently; and by temperature controlling taking advantage of the characteristic of the NTC element, the effect of safety protecting can be obtained, the inventor thereby developed the present invention based on his experience of years and nonstop study as well as improvement.